#include <stdio.h>


int main(int argc,char *argv[])
{
	int a;
	int b;
	scanf("%d",&a);
	int do_sum(int data)
	{
		int i = 0;
		int result = 0;
		if(data % 2 == 1)
		{
			for(i=1;i<= data;i+=2)
				result += i;
		}
		else if(data % 2 ==0)
		{
			for(i=0;i <= data;i+=2)
			{
				result += i;
			}
		}
	return result;
	}

	b = do_sum(a);
	printf("b= %d\n",b);

	return 0;
}
